Conventional non-fluidized bed coffee roasting equipment uses a roasting atmosphere at a temperature often exceeding 1000.degree. F. In addition, conventional non-fluidized bed roasters typically use low weight ratios of roasting atmosphere to coffee beans (hereinafter referred to as the air to bean ratio). The combination of the high roasting temperature and the low air to bean ratio results in a temperature gradient from bean to bean as well as within the coffee bean itself. Such a temperature gradient indicates that different roasting reactions occurs at different times among the beans as well as internally in any given coffee bean.
Fluidized bed roasting of coffee beans is well established in the art. For example, U.S. Pat. No. 4,169,164 to Hubbard et al. describes a two-stage fluidized bed roasting process wherein the temperature in the first stage is 450.degree. to 470.degree. F., while in the second stage roasting is at about 540.degree. F. with a fluidized bed depth of about 2 inches. A similar process is disclosed in U.S. Pat. No. 4,322,447 to Hubbard wherein the temperature in both stages is between 550.degree. and 570.degree. F. The apparatus contemplated for use in both disclosures is a fluidized bed wherein heated gas is directed downwardly through jets onto a vibrating gas-impervious plate which gas is then deflected upward, thereby fluidizing and roasting the coffee beans. The apparatus is more fully described in U.S. Pat. No. 3,229,377 to Hoyt. Numerous modifications of the apparatus are disclosed in U.S. Pat. Nos. 3,262,217; 4,109,394; 4,169,322; 4,201,499 and 4,306,359.
Other apparatus for the fluidized bed roasting of coffee are U.S. Pat. No. 3,964,175 to Sivitz which in turn contains an extensive survey of prior art attempts at fluidized bed roasting.
PCT Published International Application No. PCT/US 83/01521 (International Publication No. WO 84/01271) in the names of Brown et al. describes a modest laboratory scale apparatus and method for roasting coffee beans in less than 3 minutes. The process teaches charging green coffee beans to be roasted in a roasting chamber, flowing fluid through an inlet tube for discharge as a high velocity column against the base of the chamber and deflection radially outward for upward flow at lower velocity. The high velocity column of fluid produces a fluidization and toroidal recirculation of the coffee beans in the roasting chamber. The combination of the thermal convection and thermal conduction between individual coffee beans in the roasting chamber provides a short time uniform roast.
It is an object of the present invention to provide coffee roasting methods which are commercial and transcend all of the foregoing processes in permitting the roast to occur in less than 3 minutes while at the same time producing quite acceptable coffee.
It is another object to the present invention to provide a roasting method which produces a less dense coffee having perceived flavor and strengths and soluble solids yield significantly greater than those of conventionally roasted coffee of equivalent quality. Indeed the roaster yield of the coffee is increased significantly, the term yield referring to the pounds of roast material obtained per pound of green coffee.
It is a specific object of the present invention to provide a method for continuously roasting coffee in a manner wherein the residence time within the roaster is precisely controlled and is much less than 3 minutes and more commonly has a total roasting time of less than 2 and advantageously less than 1.5 minutes.
Still another specific objective is the ability to roast coffee by first elevating the charge of coffee with a preferred air temperature of at least 500.degree. F., depending upon the air-to-bean ratio, the bean type and the product so desired, whereafter a second roasting occurs generally at an equal or reduced temperature which may broadly be said to be 150.degree. F. or less depending upon bean variety and blend as well as feed rate, residence time, air flow and the air temperature of the first zone.
Still other specific objectives of the present invention are to provide a continuous roasting apparatus to meet the objectives of the invention including means whereby the bed of coffee may be adjusted for receipt of the roasting gas.
Still another specific object of the present invention is to provide a coffee of acceptable flavor and color and having a roasted whole bean density of 0.34 grams per cc or less and typically in the range of between 0.280 and 0.335 grams per cc.